Technical Field
The present invention relates to an inkjet recording method and an inkjet recording device.
Description of the Related Art
In inkjet recording methods, ink droplets are discharged from extremely fine nozzles and attached to a recording medium to form texts and images. This method is advantageous and diffusing since full colorization is easy and high resolution images can be obtained by a simple device in comparison with other recording methods.
Ink for use in such an inkjet recording method is demanded to have various characteristics. In particular, discharging stability of ink discharged from a head greatly affects the image quality.
In the inkjet recording method described above, pressures applied to the ink are fluctuated to discharge ink droplets.
More specifically, a meniscus is formed inside a nozzle of a head filled with ink. In normal state (stationary condition), the meniscus forms a bridge on the side of a liquid chamber with a nozzle edge as a reference point. However, when the ink in the nozzle receives a positive pressure as the pressure changes during discharging, the meniscus collapses and the ink may overflow outside the discharging orifice of the ink. In addition, fine ink mist may be developed when tails of ink droplets discharged are broken off or ink crashes on a print target resulting in scattering and such mist tends to adhere to the surface of the nozzle plate. The ink overflowing from the discharging orifice and the ink mist attached to the surface of the nozzle plate form an ink pool on the surface of the nozzle plate. If this pool contacts an ink droplet at the time of discharging, the meniscus is made uneven or the ink droplet is pulled back. For this reason, the discharging direction may be deviated. Furthermore, in a case of ink using a pigment as a coloring agent, the pigment as a solid portion is dispersed in a solvent. When the ink attached to the surface of the nozzle plate is dried, the solid portion is firmly fixed thereon, causing nozzle clogging in the end.
As describe above, in the inkjet recording method, keeping the site around the nozzle clean is demanded to secure stable dischargeability. Therefore, in general, to prevent ink contamination on the surface of the nozzle plate, a repellent film is formed on the surface to easily repel the ink or the surface is regularly wiped off to remove the ink thereon.
However, such a repellent film is known to be peeled off from the surface of the nozzle plate little by little due to wiping, etc.
Ink tends to adhere to the site where the repellent film is peeled off, which makes discharging unstable. As a consequence, ink deviation (incorrect ink discharging) and streaks occur to printed matter, which degrades the image quality. In addition, depending on the property of ink, the ink strongly sticks to the surface of the nozzle plate, so that the ink is not easily removed by wiping. In particular, when ink having a low static surface tension is discharged from a head, ink displacement and streaks occur to printed matter at sites where the repellent film is peeled off, which has an adverse impact on the image quality.
However, when the repellent film formed on the surface of a nozzle plate is degraded, there is still room for improvement to stably discharge ink having a large difference between the dynamic surface tension and the static surface tension in conventional methods.